(CNN) -- We first met Sarah Palin as the exuberant governor of Alaska, who captivated previously unenthusiastic Republicans with her brash convention speech.

CNN senior political analyst Gloria Borger says John McCain has failed to capitalize on Sarah Palin.

Unafraid to take on anyone -- Barack Obama, Democrats, special interests, the "good ol' boy" network -- she had political appeal, particularly with those conservatives who were lukewarm about John McCain.

Even some Hillary Clinton supporters, angry that Clinton was not Obama's running mate, were willing to give her a shot. She was, after all, a woman, and she seemed to be an interesting, if not unorthodox, choice.

In one bold stroke, John McCain threw away his "experience" argument in favor of reclaiming the "reform" mantle. To call it a gamble is an understatement; it was a crapshoot, with all the chips on one roll of the dice.

Then they decided to get really careful. And now Sarah Palin has become the first sequestered vice presidential candidate in American history.

And when she isn't being hidden as she crams for her vice presidential debate, she has been let into public view for selective interviews and photo-ops that have been alternately silly, painful to watch and sometimes even alarming. Watch how Palin may be turning into a liability »

Republicans are watching what once may have seemed like a brilliant idea turn into a riskier proposition each day.

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The original McCain campaign reaction to questions about Palin's qualifications was to complain the "media elite" were treating this nominee badly, with different standards, because a) she's a woman and b) she's an outsider. They then raised the point that she's got more managerial experience than Obama. All were plausible arguments (at least in the heat of a campaign).

But their case for Palin has been evaporating with remarkable speed. The more they hide her, each venture out into the open becomes magnified -- and her last attempts at tête-à-tête interviews have been disasters.

And that's the word Republicans use.

It wasn't just her interview with Katie Couric in which she tried to explain how Russia's being Alaska's "next door neighbor" adds to her foreign policy cred. (In a "Saturday Night Live" skit, Tina Fey used Palin's exact words to mock her. Yikes.)

And how about, after the first presidential debate, when she told reporters that "McCain did awesome." Cringe.

So now the McCain campaign has a real problem. They've managed to turn a self-confident and appealing candidate into one who is afraid of veering off her talking points. She's clearly studying and cramming, but it's like trying to cram for an exam when you haven't really taken the class.

And the more mistakes she makes on her scarce public outings, the more self-assurance she loses. Each mistake becomes magnified, so one mistake could be deadly.

Sure, what this all means is that the threshold for her performance in the upcoming debate is low. And Joe Biden has proved he can match her gaffes. But he's an experienced senator, with huge foreign policy credentials.

Without her self-confidence, and with her limited experience, Palin is now looking like a risk that may not pay off.